I just got google fiber and when I hook my desktop to the Ethernet I get around 700 mbps down and upload. However my nuc is getting 250 to 350 max. Not a big issue I am just currious if this a hardware limitation as well as hear others experience.

The bottleneck could be the router, a consumer router hardly can manage 700Mbps. A Netgear R7000 has NAT-LAN routing capability around 450Mbps (Stock Firmware). To get full advantage of you excellent line I would suggest server grade router.